<p>稀疏数组搜索。有个排好序的字符串数组，其中散布着一些空字符串，编写一种方法，找出给定字符串的位置。</p>

<p><strong>示例 1：</strong></p>

<pre>
<strong> 输入：</strong>words = ["at", "", "", "", "ball", "", "", "car", "", "","dad", "", ""], s = "ta"
<strong> 输出：</strong>-1
<strong> 说明：</strong>不存在返回-1。
</pre>

<p><strong>示例 2：</strong></p>

<pre>
<strong> 输入</strong>：words = ["at", "", "", "", "ball", "", "", "car", "", "","dad", "", ""], s = "ball"
<strong> 输出</strong>：4
</pre>

<p><strong>提示:</strong></p>

<ol>
	<li>words的长度在[1, 1000000]之间</li>
</ol>
